A broad climatology of very high latitude ((Formula presented) ) substorms: An update

In the process of transient solar wind energy transfer into the near-Earth environment, extremely intense currents are often observed in the nightside polar ionosphere. Auroral brightening is generally accompanied with the current intensification. The westward electrojet leads to a sharp magnetic field depression in the horizontal component around (Formula presented) magnetic latitude in the midnight meridian. It typically marks the onset of a geomagnetic substorm. During the course of a substorm, the auroral electrojet expands in local time and also poleward from the location of onset. In our earlier study Singh et al. (2012), we presented the magnetic signatures of the polar substorms using about 100 days data from the Indian Antarctic station - Bharati (CGM coordinates (Formula presented) S, (Formula presented) E) in conjunction with the data from a near-conjugate station Hornsund (CGM coordinates (Formula presented) N, (Formula presented) E) in the Arctic. This study utilizes long-term (2013–22) magnetic field observations from the same stations. It is observed that the westward electrojet (WEJ) often expands to about (Formula presented) magnetic latitudes in both hemispheres. A modified version of Newell and Gjerloev (2011) algorithm has been used to identify substorm-like WEJ intensification (hereafter substorm) over the stations. Their characteristics over a time scale of the solar cycle to the diurnal have been investigated. The hemispherical comparison of the time of onset, and occurrence and intensity of substorms with the solar illumination of the ionosphere has been carried out.